1. Field of the Invention
The present invention relates to a lockup device for a fluid-type torque transmission device. More specifically, the present invention relates to a lockup device provided in a fluid-type torque transmission device equipped with a front cover having a friction surface, an impeller that is fixed to the front cover and forms a fluid chamber, and a turbine arranged opposite the impeller inside the fluid chamber.
2. Background Information
A conventional torque converter has three types of bladed wheels (an impeller, a turbine, and a stator) arranged therein. A torque converter is one type of fluid-type torque transmission device because it transmits torque through a fluid enclosed therein. A torque converter is often provided with a lockup device. The lockup device is usually disposed in the space between the turbine and the front cover inside the fluid chamber formed by the front cover and the impeller. The lockup device is a mechanism that serves to couple mechanically the front cover and the turbine together such that torque can be transmitted directly from the front cover to the turbine. A conventional lockup device has a circular disc-shaped piston, a drive plate, a driven plate, and a torsion spring. The piston can be pressed against the front cover. The drive plate is fixed to an outer circumferential part of the piston. The driven plate is fixed to the turbine. The torsion spring serves to couple the drive plate and the driven plate together elastically in the rotational direction. The torsion spring is supported at both rotationally facing ends and at its outside circumference by either the drive plate or the driven plate. The torsion spring is also supported at both rotationally facing ends by either the driven plate or the drive plate (whichever does not support the outside circumference of the torsion spring).
When the lockup device is engaged, torque is transmitted from the front cover to the piston and from the piston to the turbine through the torsion spring. The torsion spring is compressed in the rotational direction between the drive plate and the driven plate and acts to absorb and damp torsional vibrations.
There have already been proposals for a lockup device that has a plurality of friction surfaces to increase the torque transmission capacity. One such device has an elastic coupling mechanism joined to the turbine, a drive plate that serves as the input part of the elastic coupling mechanism, a clutch plate provided with a friction coupling part, and a piston that serves to press the friction coupling part of the clutch plate against the front cover. The clutch plate is disposed so as to be sandwiched axially between the piston and the front cover. The elastic coupling mechanism of the lockup device chiefly has the drive plate, a torsion spring, and a driven plate. The drive plate is made of two plates arranged on both axially facing sides of the driven plate and supports the outside circumference and rotationally facing ends of the torsion springs with window parts that are formed therein so as to be arranged circumferentially. The driven plate has angled holes formed therein so as to correspond to the window parts in the drive plate. The torsion springs can be compressed in the rotational direction between the rotationally facing edges of the window parts of the drive plate and the rotationally facing edges of the angled holes of the driven plate. The clutch plate is fixed to the outside edge parts of the drive plate or, more specifically, the outside of the drive plate that corresponds to the window parts in the radial direction.
There is a demand for increasing the capacity of this kind of lockup device to absorb and damp torsional vibrations. One feasible way of meeting this demand is to position the torsion springs further to the outside in the radial direction. However, the drive plate has window parts for holding the torsion springs and bearing their centrifugal loads and the clutch plate is fixed to the drive plate at a portion located radially to the outside of the window parts. Consequently, it is difficult to move the radial position of the torsion springs further to the outside. Thus, the torsional vibration absorbing/damping capacity of the lockup device cannot be increased.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a lockup device provided for a fluid-type torque transmission device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.